Reactions to drugs are common and often produce an eruption. Almost any drug can result in any reaction, although some patterns are more common with certain drugs. Not all reactions are ‘allergic’ in nature. Aetiopathogenesis Drug-induced skin reactions have several possible mechanisms: ● Deposition of the drug (or metabolites) in the skin, e.g. gold. ● Excessive therapeutic effect , e.g. bruising purpura with anticoagulants. ● Immune…

Skin signs are seen with many internal disorders and are not uncommonly their presenting feature. The astute dermatologist can recognize undiagnosed systemic disease. Skin changes are common in pregnancy ( Chapter 69 ). Sometimes itch alone is the primary symptom. Skin signs of endocrine and metabolic disease Almost all endocrine diseases (and several metabolic defects) have cutaneous signs that depend on the over- or underproduction of…

Vasculitis and the reactive erythemas are characterized by inflammation within or around blood vessels. This may result from a type III hypersensitivity response, with circulating immune complexes, but other mechanisms are also possible. Vasculitis Vasculitis is a disease process usually centred on small or medium-sized blood vessels. It is often due to circulating immune complexes (CICs). Aetiopathogenesis The CICs, which may be associated with several conditions…

The inflammatory disorders of connective tissue often affect several organs, as in systemic lupus erythematosus (LE), but they may also involve the skin alone (e.g. discoid LE). Autoantibodies are a feature of these diseases, which can thus be regarded as ‘autoimmune’ Therefore, testing for the presence of autoantibodies including antinuclear antibody (ANA) staining (p. 163), double stranded (ds) or single stranded (ss) deoxyribonucleic acid (DNA) antibodies,…

Blistering is often seen with skin disease. It is found with common dermatoses such as acute contact dermatitis, pompholyx, herpes simplex, herpes zoster and bullous impetigo, and it also occurs after insect bites, burns and friction or cold injury. The type of blister depends on the level of cleavage: subcorneal or intraepidermal blisters rupture easily, but subepidermal ones are not so fragile ( Fig. 44.1 ).…

Urticaria (hives) is a common eruption characterized by wheals and angioedema. Wheals arise due to acute dermal oedema from extravascular leakage of plasma, whereas oedema deeper in the dermis and subcutis is known as angioedema. A classification is shown in Table 43.1 . Table 43.1 Classification of urticaria and angioedema Allergic (IgE-mediated) mast cell degranulation Systemic Skin contact Food, drugs, latex (aerosols) Animal saliva, pollen, latex…

Skin colour is due to a mixture of the pigments melanin (p. 8), oxyhaemoglobin (in blood) and carotene (in the stratum corneum and subcutaneous fat). Pigmentary diseases are common and particularly distressing to those with darker skin. Disorders of pigmentation mainly involve melanocytes, but other causes are mentioned where relevant. Hypopigmentation Pigment loss may be generalized or patchy. Generalized hypopigmentation occurs with albinism, phenylketonuria and hypopituitarism;…

Leg ulcers affect 1% of the adult population and account for 1% of dermatology referrals. They are twice as common in women as in men and are a major burden on the health service. Just over one-half are venous, one-tenth arterial, one-twentieth diabetic and a quarter ‘mixed’—due to venous and arterial disease. The remainder are due to rare causes. Venous disease Damage to the venous system…

Blood vessel disorders Erythema Erythema is redness of the skin, usually due to vasodilatation ( Table 40.1 ). It may be localized, e.g. with pregnancy or liver disease (on palms), fixed drug eruption and infection (e.g. Lyme disease), or generalized, as with drug eruption, toxic erythema (e.g. viral exanthem) and connective tissue disease. Table 40.1 Classification of blood vessel and lymphatic disorders Vessel Process Resulting lesion…

Congenital disease A number of usually rare congenital conditions can affect the nails. In nail – patella syndrome , the nails (and patellae) are absent or rudimentary. The nails in pachyonychia congenita are thickened and discoloured from birth. Racket nail , characterized by a broad short thumbnail, is the commonest congenital nail defect. It is dominantly inherited and more common in women. Nail dystrophy is a…

Hair loss (alopecia) The division of alopecia into diffuse, localized and scarring or non-scarring helps in diagnosis ( Table 38.1 ). Hair loss from whatever cause (and also excessive hair) can result in psychological distress in both sexes. Scalp hair is an integral part of a person’s self-image and ‘face to the world’; hence the considerable amount spent on hairdressing and hair cosmetics. Table 38.1 Causes…

Rosacea Rosacea is a chronic inflammatory facial dermatosis characterized by erythema and pustules, often associated with flushing. The cause of rosacea is unknown. Histologically, dilated dermal blood vessels, sebaceous gland hyperplasia and an inflammatory cell infiltrate are seen. Sebum excretion is normal. Aetiopathogenesis The cause of rosacea is still unknown although it is recognized that dysregulation of the innate immune system, overgrowth of commensal organisms (…

Acne Acne is a chronic inflammation of the pilosebaceous units, producing comedones, papules, pustules, cysts and scars. It affects nearly every adolescent. Acne has an equal sex incidence and tends to affect women earlier than men, although the peak age for clinical acne is 18 years in both sexes. There can be a familial tendency. Acne results from: ● increased sebum excretion—seborrhoea (greasy skin) ● pilosebaceous…

Infestation is defined as the harbouring of insect or worm parasites in or on the body. Worms—on or in the skin—are infrequent except in tropical countries. Insect life on the skin is usually transient in temperate climes, although a mite ( Demodex folliculorum ) may live harmlessly in facial hair follicles. Insects cause a variety of skin reactions ( Table 35.1 ). Contact with an insect…

Infections constitute one of the biggest problems in dermatology in tropical countries of the developing world. However, tropical infections may also be seen in countries in which they are non-endemic—among visitors and immigrants, or when acquired abroad by the indigenous population. Leprosy Leprosy is a chronic disease caused by Mycobacterium leprae. This is an acid- and alcohol-fast bacillus that cannot be cultured in the laboratory. Nasal…

Yeasts such as Malassezia and Candida albicans exist as commensals and form a normal part of the skin microbiome, where they cause minimal inflammation in the skin. Other fungi such as dermatophytes actively digest keratin and induce significant inflammation ( Chapter 32 ). Yeast infections are most commonly seen in situations where the host immune system is compromised (e.g. immunosuppressive treatment, HIV). Seborrhoeic dermatitis Seborrhoeic dermatitis…

Fungal infection in humans is common and mainly due to two groups of fungi: ● Dermatophytes : multicellular filaments or hyphae ● Yeasts : unicellular forms that replicate by budding. These are usually confined to the stratum corneum, but deep mycoses invade other tissues (p. 77). Yeast infections are described in Chapter 34 . Dermatophyte infections Dermatophytes can be divided into those that spread from human-to-human…

Immunodeficiency results from absence or failure of one or more elements of the immune system. It may be acquired, e.g. acquired immune deficiency syndrome (AIDS), or inherited, e.g. chronic mucocutaneous candidiasis. Human immunodeficiency virus disease Infection with HIV is a progressive process that mostly leads to the development of AIDS. Aetiopathogenesis HIV1 and HIV2 (the latter mainly found in West Africa) are retroviruses which incorporate into…

Herpes simplex Herpes simplex is a very common, acute, self-limiting vesicular eruption due to infection with Herpesvirus hominis . Aetiopathogenesis and pathology Herpes simplex virus is highly contagious and is spread by direct contact with infected individuals. The virus penetrates the epidermis or mucous membrane epithelium and replicates within the epithelial cells. After the primary infection, the latent non-replicating virus resides mainly within the dorsal root…

Unlike bacteria and yeasts, viruses are not thought to exist on the skin surface as commensals. However, studies in patients with viral warts have shown viral DNA in epidermal cells of seemingly normal skin next to warty areas. Viral warts Warts (verrucae) are common and benign cutaneous tumours due to infection of epidermal cells with human papillomavirus (HPV). Aetiopathogenesis and pathology More than 100 subtypes of…